Saving and/or encoding problems with KBibTeX

Saving and/or encoding problems with KBibTeX

I'm having a serious problem using KBibTeX. I create a .bib file from
Mendeley, then open it in KBibTeX. I also added some references from the
web, using the Export to BibText option from Google Scholar. So,
everything looks fine, but when I click on each entrance, some characters
change (when the source there are diacritics, like í or ñ) and a lot of
strange characters are added. The same happens between the page numbers: a
string of weird characters is added: Here is how it looks

When I modified the source (by deleting those characters and write the
diacritic as in LaTex (for example \'{a} or \~(n), which, btw, works on my
.tex), apply changes and then press OK, everything looks (sort of) fine
again. But then, when I click on the changed entrance, the same weird
characters appear again.
Not modified source:
@article{rodriguez2008acquisition,
author = "Miguel
Rodríguez-Mondoñedo",
journal = "Probus",
number = "1",
pages = "111–145",
title = "{The acquisition of differential object marking in Spanish}",
volume = "20",
year = "2008"
}
Modified by me (applied and saved changes):
@article{rodriguez2008acquisition,
author = "Miguel Rodr\'{i}­guez-Mondo\~{n}edo",
journal = "Probus",
number = "1",
pages = "111-145",
title = "{The acquisition of differential object marking in Spanish}",
volume = "20",
year = "2008"
}

And when I open the source again, this is what I get:
@article{rodriguez2008acquisition,
author = "Miguel Rodrí­guez-Mondoñedo",
journal = "Probus",
number = "1",
pages = "111–145",
title = "{The acquisition of differential object marking in Spanish}",
volume = "20",
year = "2008"
}
This happens with ALL the reference I have (like 30), either exported from
Mendeley or from the web. When I compile the .tex using Quick Build and
BibTeX in LateX, this is what I get:


These are the packages I'm using (although I don't think the problem comes
from LaTeX)
\usepackage{longtable}
\usepackage[pdftex]{graphicx}
\usepackage{lscape}
\usepackage{apacite}
\usepackage{booktabs}
\usepackage{tabularx}
\usepackage[english]{babel}
\usepackage{amsmath}
\usepackage{covington}
\usepackage{upgreek}
\usepackage{selinput}
\usepackage[margin=10pt,font=small,labelfont=bf,
labelsep=endash,position=top]{caption}
As you can see, the page numbers in the PDF appear like a string of
numbers. There is no '-' separating them. I have seen problems with
special characters, like the diacritics, but with numbers? I don't really
know what is happening. I'm using KBibTeX version 0.4, KDE Development
Platform 4.8.4 (4.8.4) on a Linux OS. I have checked other forums,
websites, but couldn't find something similar.
I need to fix this, otherwise my bibliography section is a complete mess.
Please, help!
Thanks in advance!